What is a Pure Substance?

  • A pure substance contains only one type of particle and has consistent properties throughout. Examples: salt, water.
  • Everyday consumables labeled “pure” (like milk or juice) are actually mixtures, as they contain multiple components.

What is a Mixture?

  • Mixtures are combinations of two or more pure substances. They can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).
  • Example of mixtures:
    • Homogeneous: Salt in water, sugar in tea.
    • Heterogeneous: Soil, oil and water, sand in water.

Types of Mixtures

  1. Homogeneous Mixtures (Solutions)
    • Uniform composition throughout.
    • Components cannot be distinguished with the naked eye.
    • Example: Lemonade, soda water, air (gas in gas).
    • Solution: A homogeneous mixture of solute and solvent.
      • Solute: The substance being dissolved (e.g., sugar).
      • Solvent: The substance that dissolves the solute (e.g., water).
      • Properties: Cannot scatter light, stable, particles are smaller than 1 nm.
  2. Heterogeneous Mixtures
    • Non-uniform composition, where different components can be observed.
    • Example: Sand and salt, oil and water.
    • Suspension: A type of heterogeneous mixture where particles are suspended but visible to the naked eye.
      • Properties: Particles settle over time, scatter light (Tyndall effect), can be separated by filtration.
  3. Colloidal Mixtures
    • A mixture where particles are dispersed but not dissolved, and appear homogeneous.
    • Colloid: Particles between the size of solution particles and suspension particles.
    • Examples: Milk, ink, fog, and blood.
    • Tyndall Effect: Colloids scatter light, making the path of light visible.
      • Properties: Particles do not settle, cannot be separated by filtration, but can be separated by centrifugation.

Concentration of Solutions

  • The concentration of a solution refers to the amount of solute present in a given quantity of solvent or solution.
  • Types of Concentration:
    1. Mass by Mass Percentage: Mass of SoluteMass of Solution×100\frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100Mass of SolutionMass of Solute​×100
    2. Mass by Volume Percentage: Mass of SoluteVolume of Solution×100\frac{\text{Mass of Solute}}{\text{Volume of Solution}} \times 100Volume of SolutionMass of Solute​×100
    3. Volume by Volume Percentage: Volume of SoluteVolume of Solution×100\frac{\text{Volume of Solute}}{\text{Volume of Solution}} \times 100Volume of SolutionVolume of Solute​×100

Saturated vs. Unsaturated Solutions

  • Saturated Solution: Contains the maximum amount of solute that can dissolve at a given temperature.
  • Unsaturated Solution: Can dissolve more solute at the current temperature.

Properties of Different Types of Mixtures

  1. Solution:
    • Homogeneous, particles are small (less than 1 nm), do not scatter light, and cannot be separated by filtration.
  2. Suspension:
    • Heterogeneous, particles are large enough to be seen and settle over time. They scatter light and can be separated by filtration.
  3. Colloid:
    • Heterogeneous but appears homogeneous, particles are intermediate in size. They scatter light (Tyndall effect) and do not settle easily.

Extra Knowledge

  • Latent Heat of Fusion: Heat needed to change a substance from solid to liquid at its melting point.
  • Latent Heat of Vaporization: Heat required to change a liquid to gas at its boiling point.
  • Centrifugation: A technique to separate colloidal particles based on their density, commonly used in laboratories.

Physical Properties:

  • Physical properties are those that can be observed without changing the substance’s chemical composition. These include color, hardness, texture, density, boiling point, melting point, and more. For example, the state of matter (solid, liquid, gas) can change, but the chemical composition of the substance stays the same.
  • Example: Water, ice, and steam are different in appearance and physical properties (like density and temperature), but they all consist of the same chemical substance (H₂O).

Chemical Properties:

  • Chemical properties refer to how a substance reacts with other substances, leading to a change in chemical composition. During a chemical change, new substances are formed. Example: When oil burns, it reacts with oxygen, producing carbon dioxide and water, which are chemically different from the original oil.

Physical vs. Chemical Changes:

  • Physical change: No new substances are formed. The substance may change shape, state, or appearance, but its chemical composition remains the same.
    • Example: Melting butter, boiling water, and cutting trees are physical changes.
  • Chemical change (chemical reaction): A new substance is formed, and the chemical composition of the substance changes.
    • Example: Rusting of iron, burning wood, or the reaction between vinegar and baking soda.

Types of Pure Substances:

  1. Elements:
    • An element is a pure substance made up of only one kind of atom. It cannot be broken down into simpler substances by chemical means.
    • Examples: Gold, oxygen, and iron.
    • Elements are classified into metals, non-metals, and metalloids.
  2. Compounds:
    • A compound is made from two or more elements chemically combined in a fixed ratio.
    • Example: Water (H₂O) is a compound made of hydrogen and oxygen in a 2:1 ratio.
    • Activity: When iron filings and sulfur powder are mixed and heated, a chemical reaction occurs, forming a new compound (iron sulfide) with different properties than the original elements.

Metals, Non-Metals, and Metalloids:

  • Metals:
    • They are shiny, conductive, malleable, and ductile.
    • Examples: Iron, copper, gold, etc.
  • Non-Metals:
    • Non-metals are not shiny, do not conduct heat or electricity well, and are brittle.
    • Examples: Oxygen, carbon, and iodine.
  • Metalloids:
    • Metalloids have properties that are intermediate between metals and non-metals.
    • Examples: Silicon, boron, and arsenic.

Compounds and Mixtures:

  • Mixtures: A mixture is made up of two or more substances physically combined. The components can be separated by physical means.
  • Compounds: A compound is a substance where two or more elements are chemically combined and cannot be separated by physical methods.

Key Points on Elements and Compounds:

  • More than 100 elements are known, with 92 naturally occurring.
  • Majority of elements are solid at room temperature, except for 11 gases and 2 liquids (Mercury and Bromine).
  • Gallium and Cesium become liquid just above room temperature (303 K).

Summary of Physical and Chemical Nature of Matter:

  • Physical Changes: Do not form new substances, e.g., melting butter or boiling water.
  • Chemical Changes: New substances are formed, e.g., rusting of iron, burning wood.

Additional Insights for Competitive Exams:

  • Classification of Matter: Matter is classified into pure substances (elements and compounds) and mixtures. This classification helps in understanding the behavior of matter and its changes under various conditions, which is crucial for solving questions in chemistry.
  • Understanding Reactions: It’s essential to know the difference between physical and chemical changes for identifying types of reactions in competitive exams, as many questions are based on distinguishing between these changes.
  • Examples in Daily Life: Many everyday examples (like cooking, burning, or dissolving substances) involve physical or chemical changes. Recognizing these in competitive questions helps in applying theoretical concepts to practical situations.

THESE ALL ARE THE NOTES OF CHAPTER 2 SCIENCE. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊